Which of the following alkylating agents is a nitrogen mustard derivative that requires hepatic activation to form active metabolites?

Explanation

## Cyclophosphamide: Structure and Activation **Key Point:** Cyclophosphamide is a nitrogen mustard derivative that is a prodrug requiring hepatic metabolism via cytochrome P450 enzymes (primarily CYP2C9 and CYP3A4) to generate active alkylating metabolites, particularly phosphoramide mustard. ### Mechanism of Activation Cyclophosphamide undergoes a two-step hepatic activation: 1. **Oxidation** by hepatic microsomal enzymes → hydroxycyclophosphamide 2. **Spontaneous degradation** → phosphoramide mustard (active form) + acrolein (toxic byproduct) ### Clinical Significance The acrolein metabolite is responsible for **hemorrhagic cystitis**, a dose-limiting toxicity. This is why adequate hydration and mesna (a uroprotective agent) are used during cyclophosphamide therapy. **High-Yield:** Cyclophosphamide is unique among alkylating agents because it requires hepatic activation—it is inactive in its parent form. This is why it must be given systemically (IV or oral) and why hepatic dysfunction can reduce efficacy. ### Comparison with Other Alkylating Agents | Agent | Class | Activation Required | Route | Major Toxicity | |-------|-------|---------------------|-------|----------------| | Cyclophosphamide | Nitrogen mustard | Yes (hepatic) | IV/PO | Hemorrhagic cystitis | | Cisplatin | Platinum | No (direct) | IV | Nephrotoxicity, ototoxicity | | CCNU (Lomustine) | Nitrosourea | Minimal | PO | Delayed myelosuppression | | Busulfan | Alkyl sulfonate | No (direct) | PO/IV | Pulmonary fibrosis | **Clinical Pearl:** The requirement for hepatic activation makes cyclophosphamide useful in treating both malignancies and autoimmune conditions (e.g., lupus nephritis, vasculitis) where its immunosuppressive effects are beneficial.